Powdered ceramic raw materials and other inorganic powdered materials are often shipped in bulk great distances. During such transportation, the powder agglomerates and often the agglomerates become compacted. Once the bulk "powders" reach their destination, there is typically a need for the powders to exhibit good dry flow characteristics so that they can be transferred to different receptacles for storage until such time as they are to be used.
In addition, the key to making high quality homogeneous green ceramic bodies is to have a high density with oxide ceramic particles as nearly perfectly packed as practical. Attaining such a high density requires an excellent dispersion of the particles in the solvent(s) used to make a slip from which the green ceramic body is formed.
One can only obtain maximum green density with maximum sediment density which results in a correspondingly dense cast slip having optimum packing of particles. To obtain optimum packing one must use particles with as narrow a size distribution as possible, allow them to settle slowly out of suspension and to do so without agglomeration. To prevent agglomeration, the dispersant generates repulsion between adjacent particles. Such repulsion is provided by a mechanism referred to as "charge stabilization". An alternative is to provide "steric stabilization" by which polymers attach to particle surfaces forming "clouds" around the particles. When particles approach each other, the overlap of the polymer cloud provides an osmotic pressure which keeps the particles apart.
In the past, various organics materials, such as fish oil, have been added to slips and slurries to deflocculate them and thus change their viscosity. In copending U.S. Ser. No. 07/851,610, now U.S. Pat. No. 5,252,655, a hydrolyzed siloxane was used as an addition to a ceramic slurry used to make green tape for the production of multilayer ceramic packages. The teaching of U.S. Ser. No. 07/851,610 is incorporated herein by reference.
The primary object of the present invention is to provide a new method for reducing the agglomeration of ceramic powders.
Another objective of the present invention is to provide coated ceramic particles which do not require deflocculation after the ceramic particles have been added to slips or slurries.
Another objective of the present invention is to provide a coated ceramic particle which exhibits improved dry flow characteristics.
Still another objective of the present invention is to provide a coated ceramic particle which has increased sedimentation density.
These and other objects and advantages of the present invention will be more fully understood and appreciated with reference to the following description.